1. Field of the Invention
This invention relates to circuit interrupters wherein the arc extinction is effected by utilizng an arc extinguishing fluid such as sulfur hexafluoride (SF.sub.6) gas, and in particular to circuit interrupters capable of arc extinction by an arc extinguishing fluid increased in pressure by utilizing the energy of the arc itself, wherein the withstand voltage characteristics across the separated contacts is improved to increase the arc extinguishing capability.
2. Description of the Prior Art
A typical a.c. circuit interrupter is operated by mechanically operating a pair of separable contacts at a required interrupting speed to cause the contacts to carry out a separation operation, thereby expanding an electric arc established between the separated contacts and providing a minimum interruption distance therebetween to extinguish the arc. The interruption is completed when the dielectric strength between the separated contacts is restored to a value withstanding the transient recovery-voltage within a short period of time after the extinction of the arc. However, since ionized particles stay between the separated contacts even after the extinction of the arc to degrade the voltage withstand characteristics between the contacts, it is difficult to rapidly restore the insulation characteristics between the contacts. Therefore, in order to improve the voltage withstanding characteristics between the contacts, typical circuit interrupters employ a means for flowing an arc extinguishing fluid such as SF.sub.6 gas at a great speed to promote neutralization, diffusion and exhaustion of the ionized particles.
In the conventional circuit interrupters utilizing an arc extinguishing fluid, particularly in the high-performance or heavy-duty interrupters for use under severe circuit conditions wherein the arcing time is short or the transient recovery-voltage is high, the pressure difference in the arc extinguishing fluid and the flow rate of the fluid are increased in an attempt to obtain a more effective diffusing capability. However, with such a conventional measure, a high pressure generating mechanism and associated maintenance and control apparatus are required and the structure must be made high-pressure proof, rendering the over all structure complicated, uneconomical and large-sized.